Turbomachines rely on turbines to convert fluid energy to mechanical energy. In most configurations, a turbine is connected to a shaft supported by one or more bearings where the shaft rotates along with the turbine as the turbine extracts energy from a fluid stream. For exhaust driven turbines, a shaft may rotate at over 100,000 rpm. Such rotational speeds place significant demands on bearing systems, especially as to lubrication and cooling. Often a fluid such as a natural or synthetic oil is used to lubricate as well as cool a bearing system. To ensure adequate fluid flow for lubrication and cooling, clearances between components in a bearing system should be maintained within strict limits.
Various factors impact clearances in a bearing system. These factors include machining accuracy, material properties, assembly techniques and the like. If a component cannot be machined reproducibly and accurately, then clearances may deviate from component to component and collectively from assembly to assembly. Further, if material properties allow for unacceptable wear, which may generate debris, clearances can change over time. Yet further, if an assembly technique introduces variation, then clearances from assembly to assembly may be unacceptable.
As bearing system quality has a significant impact on operation and longevity, it is important that arrangements, materials and assembly techniques be developed that can improve quality. Various exemplary arrangements, materials and techniques described herein aim to enhance quality while optionally reducing costs (e.g., manufacturing, operational, maintenance, etc.).